Method of making glass with reduced Se burnoff

ABSTRACT

A method of making glass (e.g., grey in color in some embodiments, or otherwise colored in other embodiments) in a manner so as to reduce selenium (Se) burnoff. In some embodiments, Epsom salt(s) is added to the glass batch in order to reduce Se burnoff. The resulting glass product is useful, for example, in vehicle and/or architectural privacy glass applications.

[0001] This invention relates to a method of making glass (e.g., grey ordark in color) using a technique where selenium (Se) burnoff is reducedduring the process of manufacture so as to reduce pollution. Theresulting glass compositions are thus useful, for example, in vehiclewindows and/or architectural applications.

BACKGROUND OF THE INVENTION

[0002] Privacy windows for use in automobiles and/or architecturalapplications are becoming more popular, as is demand for grey glass ingeneral. These glasses are typically based upon a standardsoda-lime-silica glass composition (used to make float glass) to whichis added various colorants to attain the desired coloring and spectralproperties. Iron, typically including both ferric (Fe³⁺) and ferrous(Fe²⁺) iron, is often used in such glasses. Ferric iron is a strongultraviolet (UV) absorber and yellow/green colorant while ferrous ironis a known infrared (IR) absorber and blue colorant. Other colorantswhich are often used in such glasses include Se, Co, Cr, Mn, V, Ce, Ti,Mo, and the like.

[0003] Commonly owned U.S. Pat. No. 5,932,502 (hereby incorporatedherein by reference) discloses a dark grey privacy glass compositionincluding a colorant portion of Fe₂O₃ (total iron), Co₃O₄, Se, andCr₂O₃. The resulting glass of the '502 patent has good coloring andspectral characteristics.

[0004] Unfortunately, when making the glass of the '502 patent a largepercentage of the Se originally added to the batch burns off during theprocess of glass manufacture (i.e., a high rate of Se burnoff isexperienced). Se is a known pollutant, and high rates of Se burnoff arethus undesirable for environmental reasons. For example, when makingglass according to the '502 patent commercially, about 0.1000% (wt. %)metallic Se is originally provided in the batch along with about 1.0%salt cake which is used as a refining agent. After the batch is meltedand processed, the resulting glass has only about 0.0026-0.0028% Se lefttherein (the rest of the Se has burned off). This translates into a Seretention of less than 10% (i.e., at least about 90% of the Seoriginally present in the batch burns off during the process ofmanufacture). This high rate/percentage of Se burnoff is undesirable.

[0005] U.S. Pat. No. 5,346,867 discusses the problem of Se vaporization.In response to the problem, the '867 patent uses manganese oxide inorder to decrease Se burnoff. Unfortunately, the MnO₂ technique used inthe '867 patent only enables up to 22.3% of the originally presented Seto be retained (see Table III in the '867 patent).

[0006] In view of the above, it will be apparent to those skilled in theart that there exists a need in the art for a method of makingSe-inclusive glass wherein the rate and/or percentage of Se burnoffduring the process of glass manufacture can be reduced and/or minimized.

SUMMARY OF THE INVENTION

[0007] An object of this invention is to provide a method of making aselenium (Se) inclusive glass in a manner such that Se burnoff duringthe process of manufacture is reduced. This method may be applied togrey colored glass in certain embodiments of this invention, as well asto other colored glasses in other embodiments of this invention.

[0008] Another object of this invention is to reduce Se burnoff in aprocess of glass manufacture by using Epsom salt(s) (e.g., MgSO₄×7H₂O)as a refining agent and/or melting aide. Surprisingly, it has been foundthat the use of Epsom salt(s) (e.g., instead of and/or in addition tosalt cake or the like) as a batch component enables more Se to beretained (i.e., less Se burnoff).

[0009] Another object is to fulfill one or more of the above-listedobjects and/or needs.

[0010] Generally speaking, this invention fulfills one or more of theabove-listed objects or needs by providing a method of making glass, themethod comprising:

[0011] processing a molten glass batch including Se in order to form aresulting glass product comprising SiO2 and Se, in a manner so that theresulting glass product retains at least 30% of the Se originallypresent prior to melting.

[0012] In other embodiments of this invention, one or more of theabove-listed needs and/or objects is/are fulfilled by providing a methodof making glass, the method comprising:

[0013] providing a glass batch including SiO2, Fe2O3, Epsom salt, and anoriginal amount of Se; and

[0014] forming a resulting glass product from the glass batch in amanner such that the resulting glass product includes at least 30% ofthe original amount of Se due at least to the presence of a sufficientquantity of the Epsom salt in the batch.

[0015] In certain other embodiments of this invention, one or more ofthe above-listed needs or objects is fulfilled by providing a method ofmaking a grey colored glass, the method comprising:

[0016] providing a molten glass batch comprising SiO2, Se, and Epsomsalt;

[0017] processing the glass batch in order to make a resulting greycolored glass product, the grey colored glass product including a baseglass portion comprising: Ingredient wt. % SiO₂ 67-75% Na₂O 10-20% CaO 5-15% MgO 0-5% Al₂O₃ 0-5% K₂O 0-5% BaO 0-1%

[0018] Ingredient Amount Total iron (expressed as Fe₂O₃): 1.0 to 2.2%(wt. %) selenium (Se): 10 to 50 ppm cobalt oxide: 0.015 to 0.040%titanium oxide: 0 to 3.5% chromium oxide: 0 to 0.03%; and

[0019] wherein the Epsom salt is provided in the glass batch insufficient quantity so that the resulting glass product retains at least30% of the Se originally present in the batch.

[0020] Certain other embodiments of this invention fulfill a desiredneed by providing a grey colored glass comprising:

[0021] a base portion and a colorant portion;

[0022] said base portion of the glass comprising: Ingredient wt. % SiO₂67-75% Na₂O 10-20% CaO  5-15% MgO 0-5% Al₂O₃ 0-5% K₂O 0-5% BaO 0-1%

[0023] and said colorant portion consisting essentially of: IngredientAmount Total iron (expressed as Fe₂O₃): 1.4 to 1.8% (wt. %) selenium(Se): 10 to 50 ppm cobalt oxide: 0.015 to 0.040% titanium oxide: 0.2 to3.5% chromium oxide: 0 to 0.03%; and

[0024] wherein the glass is grey in color and has a dominant wavelengthin the range of from 435 nm to 570 nm, is substantially free ofmanganese dioxide, and is substantially free of nickel.

DETAILED DESCRIPTION OF CERTAIN EMBODIMENTS OF THIS INVENTION

[0025] Glasses (e.g., colored grey or any other suitable color)according to different embodiments of this invention may be used, forexample, in the automotive industry (e.g., windshields, backlites, sidewindows, etc.), in architectural applications, and/or in other suitableapplications. Resulting glass products herein may be from about 1-12 mmthick in different embodiments.

[0026] Certain glasses according to this invention utilizesoda-lime-silica flat glass as their base composition/glass, to which isadded certain ingredients making up a colorant portion. An exemplarysoda-lime-silica base glass according to certain embodiments of thisinvention, on a weight percentage (wt. %) basis, includes the followingbasic ingredients: TABLE 1 EXEMPLARY BASE GLASS Ingredient Wt. % SiO₂67-75% Na₂O 10-20% CaO  5-15% MgO 0-5% Al₂O₃ 0-5% K₂O 0-5% BaO 0-1% B₂O₃0-5%

[0027] In certain embodiments, for example, glass herein may be madefrom batch raw materials silica sand, soda ash, dolomite, limestone,with the use of at least Epsom salt(s) as refining agent and/or meltingaide. Other minor ingredients, including various conventional refiningaids may also be included in the base glass. Additionally, in certainembodiments a spectral modifier such as sodium phosphate (Na₂HPO₄) in anamount of from 0 to 2.0%, more preferably from 0 to 1.5%, may be addedto the batch for color adjustment purposes. Sodium phosphate, while acolor modifier, is not defined as a “colorant” herein.

[0028] As explained in more detail below, the use of Epsom salts (e.g.,MgSO₄×7H₂O) in the process of glass manufacture has surprisingly beenfound to reduce Se burnoff during the manufacturing process (e.g.,conventional melt and float processing). This reduction in selenium (Se)burnoff is significant in that it both reduces pollution and/or reducesthe amount of costly Se that has to be added to the glass batch prior toor during the melt in order to end up with the same amount of Se in theresulting glass composition.

[0029] Reducing agent(s) such as Si (metallic), Si, silicon monoxide,SiO, sucrose, and/or carbon may also be used. In other embodiments ofthis invention, no reducing agent is needed due to the rather high ironcontent to be discussed more fully below. In certain embodiments of thisinvention soda-lime-silica based glasses include by weight from about10-15% Na₂O and from about 6-12% CaO. While a soda-lime-silica baseglass set forth above is preferred in certain embodiments of thisinvention, this invention is not so limited. Thus, other base glasses(e.g., borosilicate glass) may instead be employed in alternativeembodiments.

[0030] In one example embodiment of this invention, to the base glass(e.g., see Table 1 above) a colorant portion is added which causes theresulting glass to be grey in color (i.e., dominant wavelength of from435 nm to 570 nm). In this embodiment, the resulting grey glass has adominant wavelength of from 480 nm −560 nm (nanometers), and anexcitation purity (Pe) no greater than 11%, more preferably no greaterthan 8%, and most preferably from 1 to 7%. In this embodiment, anexemplary colorant portion that is added to the base glass issubstantially free of cerium, manganese dioxide, and/or nickel (i.e., nomore than 0.0030% Ce, CeO, and/or CeO₂, no more than 0.0030% Mn or MnO₂,and/or no more than 0.0010% Ni and/or NiO), and is characterized as setforth in Table 2 below (in terms of weight percentage of the total glasscomposition): TABLE 2 COLORANT PORTION ADDED TO BASE GLASS BATCH INEXAMPLE GREY GLASS EMBODIMENT Ingredient (Preferred) (More Preferred)Total iron (expressed as Fe₂O₃): 1.0 to 2.2% (wt. %) 1.2 to 1.8%selenium (Se) (metallic form): 30 to 90 ppm 40-80 ppm [or if Se added asNa₂SeO₃]: 70 to 180 ppm 90-160 ppm cobalt oxide (e.g., Co₃O₄): 0.015 to0.040% 0.018 to 0.030% titanium oxide (e.g., TiO₂): 0 to 3.5% 0.1 to2.6% chromium oxide (e.g., Cr₂O₃): 0 to 80 ppm 5-20 ppm

[0031] In certain embodiments of this invention, the colorant portion issubstantially free of other colorants (other than potentially traceamounts). As can be seen above, the colorant portion may also besubstantially free of chromium oxide, phosphates, and/or titanium oxidein certain embodiments of this invention. However, in other embodimentschromium oxide may be used to affect color. In certain embodiments, thecolorant portion consists essentially of the colorants listed in Table 2above, while in other embodiments the colorant portion simply comprisesor includes the colorants listed in Table 2 above. However, it should beappreciated that small amounts of other materials (e.g., refining aids,melting aids, and/or impurities) may be present in the glass such asmanganese, molybdenum, tin, chlorine, zinc, zirconium, Si, sulfur,fluorine, lithium and strontium, without taking away from the purpose(s)and/or goal(s) of the grey glass embodiment of the instant invention.Those of skill in the art will recognized that the aforesaid colorantportion is provided for purposes of example only, and certainembodiments of the instant invention are not so limited.

[0032] In preferred embodiments of this invention, Epsom salt(s) (e.g.,MgSO₄×7H2O) is added to the batch (e.g., including the base glass andcolorant portion in Tables 1 and 2 above) prior and/or during the meltin order to reduce Se burnoff. In one example embodiment of thisinvention, from about 0.1 to 2.0% (wt. %) Epsom salt(s) is added to thebatch, and in more preferred embodiments from about 0.2 to 1.5% Epsomsalt(s) is added to the batch. As a result of the addition of Epsomsalt(s) to the batch, at least about 30% of the original Se added to thebatch is retained in the final glass composition, more preferably atleast about 40% of the original Se added to the batch is retained in thefinal glass composition, and most preferably at least about 50% of theoriginal Se added to the batch is retained in the final glasscomposition. Another advantage associated with Epsom salts is that theydo not require a reducing agent to be used in conjunction therewith(although one may be used), which again can help reduce Se burnoff.

[0033] Selenium (Se) may be added to the batch in a variety of differentforms in different embodiments of this invention. For example, Se may beadded to the batch in the form of sodium and/or calcium selenites, ironand/or cobalt selenides, metallic Se powder, or in any other suitablemanner. Example Se powder amounts and sodium selenite amounts are shownabove in Table 2. While Se often combines with iron as iron selenide(FeSe) in glass to produce brown color, and does so in certainembodiments of this invention, selenium is referred to in the colorantportion herein as “Se” which is meant to include, for example, its stateas Se as well as its other state(s) in glass such as FeSe (and all Sevalence states). For example, Se may exist in the form of selenates,selenides, selenites, polyselenides, and/or in elemental form.

[0034] Referring to Table 2 above for example, in more preferredembodiments of this invention Se can be added to the batch as a colorantin either (a) the form of metallic Se powder, and/or (b) the form ofNa₂SeO₃. If added in the form of metallic Se powder, from about 30-90ppm (parts-per-million) is added to the batch. However, if added in theform of Na₂SeO₃, then from about 70-180 ppm of Na₂SeO₃ is added. As willbe appreciated by those skilled in the art, 60 ppm Se metallic powderhas about the same amount of Se as does 144 ppm Na₂SeO₃. A combinationof Se metallic powder and Na₂SeO₃ may be added in alternativeembodiments of this invention. As can be seen from the chart/tablebelow, the addition of Se in the form of Na₂SeO₃ helps Se retention evenmore in certain embodiments of this invention.

[0035] Regarding cobalt (Co), this blue colorant may be added to theglass batch in the amounts set forth in Table 2 above in certain exampleembodiments. Moreover, it is believed that much of the cobalt in theglass is in the oxide state of Co₃O₄. However, other oxide states of CoOare also possible in glasses according to this invention. Thus, unlessexpressly stated to the contrary, the terms “CoO” and “Co₃O₄” as usedherein include not only cobalt in this/these particular oxide state(s),but also include(s) cobalt which may be present in other oxidationstate(s).

[0036] The total amount of iron present in the glass is expressed hereinin terms of Fe₂O₃ in accordance with standard practice. This, however,does not imply that all iron is actually in the from of Fe₂O₃. Likewise,the amount of iron in the ferrous state is reported herein as FeO, eventhough all ferrous state iron in the glass may not be in the form ofFeO. The proportion of the total iron in the ferrous state (i.e., FeO)is used to determine the redox state of the glass, and is expressed asthe ratio FeO/Fe₂O₃ which is the weight percentage (%) of iron in theferrous state (expressed as FeO) divided by the weight percentage (%) oftotal iron (expressed as Fe₂O₃). Thus, Fe₂O₃ herein means total iron andFeO means iron in the ferrous state. According to certain embodiments ofthis invention, the colorant portion of the glass composition herein ischaracterized by a redox value (i.e., FeO/Fe₂O₃) of from 0.20 to 0.30,more preferably from 0.23 to 0.27.

[0037] Optionally, titanium oxide may be used in certain embodiments ofthis invention to increase IR absorption. Moreover, the use of titaniumoxide may enable the reduction and/or elimination of chromium oxide fromthe composition. Additionally, it is believed that the titanium oxidemay also help retain Se in the glass (i.e., reduce Se burnoff) bycausing it to be more evenly distributed throughout the melt.

[0038] It is noted that glass according to this invention is often madevia the known float processing in which a tin bath is utilized. It willthus be appreciated by those skilled in the art that as a result offorming the glass on molten tin in certain exemplary embodiments, smallamounts of tin or tin oxide may migrate into surface areas of the glasson the side that was in contact with the tin bath during manufacture(i.e., typically, float glass may have a tin oxide concentration of0.05% or more (wt.) in the first few microns below the surface that wasin contact with the tin bath).

[0039] When used in the automotive market, grey glasses according tocertain embodiments of this invention (e.g., at about 4 mm thickness forpurposes of reference) may have an Lta (visible transmission, Ill. A, 2degree observer) of from 10-30%, more preferably from 12-24%, mostpreferably from 13-20%; an IR transmission percentage (%) of from 3-28%,more preferably from 4-24%, and most preferably from 8-21%. With regardto transmissive color, these grey glasses according to certainembodiments of this invention may have an a* value (Ill. D65, 10 degreeobserver) of from 0.0 to −10.0, more preferably from −2.0 to −8.0, andmost preferably from −3.0 to −7.0; and a b* value (Ill. D65, 10 degreeobserver) of from −4.0 to +10.0, more preferably from 0 to +9.0, andmost preferably from +2.0 to +8.0. Herein, transmissive Lta is measuredin terms of Ill. A, 2 degree observer, while a* and b* color values aremeasured in terms of Ill. D65, 10 degree observer.

[0040] The above-listed colorant portion(s) data and base glass data arefor purposes of example only, and the instant invention is not solimited. Instead, one focus of the instant invention is the reduction ofSe burnoff during the glass manufacture process, and the use of Epsomsalts in a Se inclusive batch may be used in accordance with thisinvention in combination with base glasses and/or colorant portionsother than those discussed above.

EXAMPLES

[0041] Certain grey colored privacy glasses according to exampleembodiments of this invention were made using the following base glassbatch (note: the below-listed ingredients in the batch will add up to100% by weight once oxides thereof are accounted for; thus, they neednot add up to one hundred as raw materials): Batch Ingredient for BaseGlass Parts by Wt. % sand (SiO₂) 71.5 soda ash (Na₂CO₃) 23.7 dolomite(CaCO₃, MgCO₃) 18.32 limestone (CaCO₃) 6.1

[0042] In addition to the base glass materials above, the Epsom salt(s)and colorant portions added to the original base batch for Examples 1-13are set forth below in Table 3 along with resulting solarcharacteristics. Moreover, the amount (ppm) and percentage of originallyadded Se retained in the final glass product (after the melt andprocessing) is listed in Table 3 below. The spectral properties in Table3 (e.g., Lta, IR transmission, transmissive a*, transmissive b*) arealso for the final glass product. For each of the examples, final glassproducts were about 4.09 mm thick sheets. It is also noted that Examples3-5, 7, and 9-13 were subject to a fritting procedure where the glassmelt was poured into water, crushed and re-melted; which typicallyincreases loss of Se and decreases FeO % in the redox. As for the methodof adding Se to the original glass batch, it is noted that, for example,0.0140 wt. % Na₂SeO₃ is equivalent to and has the same amount of Se as0.0056 wt. % metallic Se powder (this is taken into account incalculating the amount of Se retained in the final glass product). TABLE3 Examples 1-13 Material/ Property Ex. 1 Ex. 2 Ex. 3 Ex. 4 Ex. 5 Ex. 6Ex. 7 Ex. 8 Ex. 9 Ex. 10 Ex. 11 Ex. 12 Ex. 13 Fe₂O₃ 1.4 1.8 1.4 1.8 1.61.8 1.8 1.8 1.6 1.2 1.25 1.6 1.25 (total iron) (rouge) TiO₂ (titania)2.6 1.1 1.0 0.6 0.6 0.6 0.6 0.6 0.2 0 0.4 0.4 0.4 Cr₂O₃ 0 0 0 0 0 0 0 00 0.01 0 0 0 Co₃O₄ 0.024 0.024 0.023 0.023 0.0235 0.025 0.025 0.0230.022 0.021 0.021 0.022 0.021 Se (ppm) 60 60 0 0 0 0 0 60 0 0 0 0 0(metallic powder) Se (ppm) 0 0 130 144 135 144 100 0 130 140 150 140 130(Na₂SeO₃) Na₂HPO₄ 0 0 0 1.0 0 1.0 0 0 0 0 1.0 0 0 Epsom 0.9 0.9 0.3 0.50.3 0.5 0.3 0.5 0.6 0.6 0.6 0.3 0.6 (MgSO₄x7H₂O) % Lta (in 19.0 13.418.87 15.81 15.45 14.9 14.1 19.7 17.03 20.0 20.7 14.75 20.6 finalproduct) % IR (in 23.5 8.2 15.7 10.7 9.43 19.8 12.4 20.9 4.6 15.7 11.87.18 12.1 final product) % FeO (wt.) 0.20 0.37 0.26 0.33 0.35 0.23 0.300.22 0.48 0.26 0.31 0.40 0.31 (final prod.) a* (trans- −3.6 −5.3 −4.1−4.8 −3.78 −1.9 −6.4 −4.2 −7.0 −3.44 −5.0 −3.7 −4.6 missive) b* (trans-+8 +8 +5.4 +6.4 +5.0 +9.1 +4.4 +4.4 −3.6 +2.43 +0.24 +5.1 +0.8 missive)Se retained 28 25 25 30 30 41 n/a 28 20 31 30 31 n/a in final (ppm) Se47% 42% 48% 52% 56% 71% n/a 47% 38% 55% 50% 55% n/a retention %

[0043] In manufacturing these example glasses referenced above, the baseglass batch material together with the colorant portion was melted in aplatinum (or alumina) crucible at 1500 degrees C. for about four hours,in a laboratory electric melting furnace. Thereafter, it was cast intographite molds, and annealed at 620 degrees C. for half an hour, andthen allowed to cool down to room temperature. The example glasses(i.e., samples) were then polished to the desired 4.09 mm thickness andspectral measurements above were taken with a Perkin Elmerspectrophotometer to determine the light transmittance in the wavelengthrange from 250 to 2,000 nm. The results are set forth in Table 3 above.It is noted that the “batch” herein can be put together prior to and/orduring the melt itself. Thus, a component/material is said to be addedto the batch regardless of whether it is added to the batch prior tomelting or during melting.

[0044] Surprisingly, as can be seen in Table 3, the percentage (%) of Seretained in the final glass product is much higher than in the priorart. This is believed to be due to the use of Epsom salt(s) instead ofor in addition to salt cake as a refining agent. In certain embodimentsof this invention, at least about 30% of the original Se added to thebatch is retained in the final glass composition, more preferably atleast about 40% of the original Se added to the batch is retained in thefinal glass composition, and most preferably at least about 50% of theoriginal Se added to the batch is retained in the final glasscomposition. Yet another surprising result illustrated in Table 3 aboveis that Se retention is improved when the Se is originally added to thebatch in the form of Na₂SeO₃ (as opposed to metallic Se powder). Forpurposes of example referring to Table 3, in Example 1 the Se retentionpercentage (%) was calculated by taking the final amount of Se found tobe in the resulting glass (i.e., 28 ppm) and dividing it by the originalamount of Se in the glass batch (i.e., 60 ppm). Thus, 28/60=47% Seretention for Example 1. In a similar manner, for Example 10 the Seretention percentage (%) was calculated by taking the final amount of Sefound to be in the resulting glass (i.e., 31 ppm) and dividing it by theoriginal amount of Se in the glass batch (i.e., 56 ppm). The originalamount of Se in the glass batch was calculated by multiplying 140 ppmNa₂SeO₃ by: (0.0056 Se/0.0140 Na₂SeO₃) [140×(0.0056/0.0140)=56 ppm Se inthe original batch]. Thus, 31/56=55% Se retention in Example 10.

[0045] Certain of the aforesaid example glasses were then x-rayanalyzed. For example, the final resulting Example 12 glass was x-rayanalyzed and its composition was determined to be as follows (note:elements such as K, Al, Cr, and Ni were not intentionally added to thebatch, but may be present nonetheless): TABLE 4 COMPOSITION OF RESULTINGEXAMPLE 12 GLASS (4 mm) Ingredient wt. % (except as otherwise stated)SiO₂ 70.17% Na₂O 13.709% CaO 9.404% MgO 4.075% Al₂O₃ 0.163% K₂O 0.095%SO₃ 0.114% TiO₂ 0.413% Fe₂O₃ (total iron) 1.569% cobalt oxide 0.0218% Se(ppm) 31 ppm Cr₂O₃(ppm) 10 ppm NiO (ppm)  6 ppm

[0046] As can be seen in Table 4, amounts of chromium oxide and NiO werein the final product, although they were not intentionally added to thebatch. Such amounts of chromium oxide, for example, may affect color inthe final glass product.

[0047] Accordingly, the resulting glass composition (after melting,processing, etc.) in certain embodiments of this invention may include abase glass portion comprising: Ingredient wt. % SiO₂ 67-75% Na₂O 10-20%CaO  5-15% MgO 0-5% Al₂O₃ 0-5% K₂O 0-5% BaO 0-1%

[0048] and a colorant portion comprising (or consisting essentially ofin certain alternative embodiments): Ingredient Preferred More PreferredTotal iron (expressed as Fe₂O₃): 1.0 to 2.2% (wt. %) 1.2 to 1.8%selenium (Se): 10 to 50 ppm 20-40 ppm cobalt oxide: 0.015 to 0.040%0.018 to 0.030% titanium oxide: 0 to 3.5% 0.1 to 2.6% chromium oxide: 0to 80 ppm 5-20 ppm

[0049] The terms, and characteristics, of ultraviolet lighttransmittance (% UV), infrared energy transmittance (% IR), dominantwavelength (DW) and excitation purity (i.e. % “purity”, or Pe) are alsowell understood terms in the art, as are their measurement techniques.Such terms are used herein, in accordance with their well known meaning,e.g., see U.S. Pat. No. 5,308,805. IR transmittance is conventionallymeasured using Simpson's Rule and Parry Moon Air Mass=2 over thewavelength range 800-2100 nm inclusive at 50 nm intervals. Dominantwavelength (DW) is calculated and measured conventionally in accord withthe aforesaid CIE Publication 15.2 (1986) and ASTM: E 308-90. The term“dominant wavelength” includes both the actual measured wavelength and,where applicable, its calculated complement. Excitation purity (Pe or %“purity”) is measured conventionally in accordance with CIE Publication15.2 (1986) and ASTM: E 308-90.

[0050] It is noted that according to different embodiments of thisinvention, glass compositions herein may be manufactured via singlebatch melting techniques, or alternatively via multiple pre-batch mixingtechniques utilizing separate pre-batch mixes that are ultimately mixedtogether to make up a final overall batch mixture. For example, in thelatter approach, one of the prebatch mixes could be made up of theiron-containing ingredient (e.g. rouge) along with optional reducingagents and some of the sand. The remaining batch ingredients can then bemade up by admixing them in another separate prebatch mix or into two ormore prebatch mixes before admixing them with the iron and reducingagent-containing first prebatch mix. After each separate prebatch mix isseparately mixed, to form a substantially homogenous powdered admixture,the two or more prebatch mixes are mixed together to form the overall(or final) batch mixture. Conventional melting and refining techniquesare then used to form a molten glass from which flat sheet glass orother articles may be formed.

[0051] In certain embodiments of this invention, the colorant portion issubstantially free of copper oxide (e.g., CuO). However, in otherembodiments of this invention, from about 0-500 ppm (more preferablyfrom about 0-200 ppm) may be provided in the glass batch and/orresulting glass article. CuO, which acts a a reddish colorant in thisregard, can be added in a manner so that the amount of Se needed can bereduced to a lower level.

[0052] Once given the above disclosure many other features,modifications and improvements will become apparent to the skilledartisan. Such features, modifications and improvements are thereforeconsidered to be a part of this invention, the scope of which is to bedetermined by the following claims:

What is claimed is:
 1. A method of making glass, the method comprising:processing a molten glass batch including Se in order to form aresulting glass product comprising SiO₂ and Se, in a manner so that theresulting glass product retains at least 30% of the Se originallypresent prior to melting.
 2. The method of claim 1, wherein saidprocessing is performed so that the resulting glass product retains atleast 40% of the Se originally present prior to melting.
 3. The methodof claim 1, wherein said processing is performed so that the resultingglass product retains at least 50% of the Se originally present in thebatch prior to melting.
 4. The method of claim 1, further comprisingadding Epsom salt to the batch in an amount sufficient to reduce Seburnoff during melting or the processing.
 5. The method of claim 4,wherein the Epsom salt comprises MgSO₄×7H₂O.
 6. The method of claim 4,further comprising adding the Epsom salt to the batch in an amount offrom 0.1 to 2.0% by weight.
 7. The method of claim 1, wherein saidprocessing is performed so that the resulting glass product comprises abase glass portion comprising: Ingredient wt. % SiO₂ 67-75% Na₂O 10-20%CaO  5-15% MgO 0-5% Al₂O₃ 0-5% K₂O 0-5% BaO 0-1%

and a colorant portion comprising: Ingredient Amount Total iron(expressed as Fe₂O₃): 1.0 to 2.2% (wt. %) selenium (Se): 10 to 50 ppmcobalt oxide: 0.015 to 0.040% titanium oxide: 0 to 3.5% chromium oxide:0 to 80 ppm.


8. The method of claim 7, wherein the glass is grey in color and has adominant wavelength in the range of from 435 nm to 570 nm.
 9. The methodof claim 7, further comprising adding from 30-90 ppm of Se metallicpowder to the batch.
 10. The method of claim 7, further comprisingadding from 70 to 180 ppm of Na₂SeO₃ to the batch, so that at least aportion of the Se is added to the batch in the form of Na₂SeO₃.
 11. Themethod of claim 7, wherein said processing is performed so that theresulting glass product includes a colorant portion comprising:Ingredient Amount Total iron (expressed as Fe₂O₃): 1.2 to 1.8% (wt. %)selenium (Se): 20 to 40 ppm cobalt oxide: 0.018 to 0.030% titaniumoxide: 0.1 to 2.6% chromium oxide: 5-20 ppm.


12. The method of claim 1, wherein said processing is performed so thatthe resulting glass product includes a base glass portion comprising:Ingredient wt. % SiO₂ 67-75% Na₂O 10-20% CaO  5-15% MgO 0-5% Al₂O₃ 0-5%K₂O 0-5% BaO 0-1%

and a colorant portion consisting essentially of: Ingredient AmountTotal iron (expressed as Fe₂O₃): 1.0 to 2.2% (wt. %) selenium (Se): 10to 50 ppm cobalt oxide: 0.015 to 0.040% titanium oxide: 0 to 3.5%chromium oxide: 0 to 80 ppm.


13. A method of making glass, the method comprising: providing a glassbatch including SiO₂, Fe₂O₃, Epsom salt, and an original amount of Se;and forming a resulting glass product from the glass batch in a mannersuch that the resulting glass product includes at least 30% of theoriginal amount of Se due at least to the presence of a sufficientquantity of the Epsom salt in the batch.
 14. The method of claim 13,further comprising forming the resulting glass product in a manner suchthat the resulting glass product includes at least 40% of the originalamount of Se.
 15. The method of claim 14, further comprising forming theresulting glass product in a manner such that the resulting glassproduct includes at least 50% of the original amount of Se.
 16. Themethod of claim 13, wherein the glass batch includes from 30-90 ppm Seand from 0.1 to 2.0% Epsom salt.
 17. The method of claim 16, wherein theresulting glass product includes from 10-50 ppm Se.
 18. The method ofclaim 13, wherein the Epsom salt comprises MgSO₄×7H₂O.
 19. The method ofclaim 13, wherein said forming is performed so that the resulting glassproduct comprises a base glass portion comprising: Ingredient wt. % SiO₂67-75% Na₂O 10-20% CaO  5-15% MgO 0-5% Al₂O₃ 0-5% K₂O 0-5% BaO 0-1%

and a colorant portion comprising: Ingredient Amount Total iron(expressed as Fe₂O₃): 1.0 to 2.2% (wt. %) selenium (Se): 10 to 50 ppmcobalt oxide: 0.015 to 0.040% titanium oxide: 0 to 3.5% chromium oxide:0 to 80 ppm copper oxide: 0 to 500 ppm.


20. The method of claim 19, wherein the resulting glass product issubstantially free of nickel (Ni) and manganese (Mn).
 21. The method ofclaim 13, wherein the resulting glass product includes from 1.0 to 2.2%total iron (expressed as Fe₂O₃), and has a redox value FeO/Fe₂O₃ of from0.20 to 0.30.
 22. The method of claim 13, wherein the resulting glassproduct has an Lta (visible transmission, Ill. A, 2 degree observer) offrom 10-30%, and an IR transmission percentage (%) of from 3-28%. 23.The method of claim 22, wherein the resulting glass product has atransmissive a* value (Ill. D65, 10 degree observer) of from 0.0 to−10.0, and a transmissive b* value (Ill. D65, 10 degree observer) offrom −4.0 to +10.0.
 24. A method of making a grey colored glass, themethod comprising: providing a molten glass batch comprising SiO₂, Se,and Epsom salt; processing the glass batch in order to make a resultinggrey colored glass product, the grey colored glass product including abase glass portion comprising: Ingredient wt. % SiO₂ 67-75% Na₂O 10-20%CaO  5-15% MgO 0-5% Al₂O₃ 0-5% K₂O 0-5% BaO 0-1%

and a colorant portion comprising: Ingredient Amount Total iron(expressed as Fe₂O₃): 1.0 to 2.2% (wt. %) selenium (Se): 10 to 50 ppmcobalt oxide: 0.015 to 0.040% titanium oxide: 0 to 3.5% chromium oxide:0 to 80 ppm;

and wherein the Epsom salt is provided in the glass batch in sufficientquantity so that the resulting glass product retains at least 30% of theSe originally present in the batch.
 25. The method of claim 24, whereinthe Epsom salt is provided in the glass batch in sufficient quantity sothat the resulting glass product retains at least 40% of the Seoriginally present in the batch.
 26. The method of claim 25, wherein theEpsom salt is provided in the glass batch in an amount of from 0.1 to2.0% by weight so that the resulting glass product retains at least 50%of the Se originally present in the batch.
 27. A grey colored glasscomprising: a base portion and a colorant portion; said base portion ofthe glass comprising: Ingredient wt. % SiO₂ 67-75% Na₂O 10-20% CaO 5-15% MgO 0-5% Al₂O₃ 0-5% K₂O 0-5% BaO 0-1%

and said colorant portion consisting essentially of: Ingredient AmountTotal iron (expressed as Fe₂O₃): 1.2 to 1.8% (wt. %) selenium (Se): 10to 50 ppm cobalt oxide: 0.015 to 0.040% titanium oxide: 0.2 to 3.5%chromium oxide: 5-20 ppm; and

wherein the glass is grey in color and has a dominant wavelength in therange of from 435 nm to 570 nm, is substantially free of manganesedioxide, and is substantially free of nickel.
 28. The glass of claim 27,wherein the glass has an excitation purity (Pe) from 1 to 7%.
 29. Theglass of claim 27, wherein the glass has a visible transmission Lta(Ill. A, 2 degree observer) of from 10-30%, and an IR transmission offrom 3-28%.
 30. The glass of claim 29, wherein the glass has atransmissive a* value (Ill. D65, 10 degree observer) of from 0.0 to−10.0, and a transmissive b* value (Ill. D65, 10 degree observer) offrom −4.0 to +10.0.
 31. A glass comprising: Ingredient wt. % SiO₂67-75%  Na₂O 10-20%  CaO 5-15% MgO 0-5%  Al₂O₃ 0-5%  K₂O 0-5%  BaO  0-1%; and

wherein the glass has a Se retention of at least 30%.